1. Field of the Invention
This invention relates to an improved ink jet head structure for use in ink jet printers.
Generally, an ink jet printing system comprises a head structure which is coupled to a reservoir of ink so that ink under pressure is discharged in a stream from the head structure. The head structure is either vibrated or periodically constricted so that a short distance from an opening in the head structure the ink stream breaks up and forms drops. A charging electrode surrounds the point of drop formation, and a succession of voltages are applied to the electrode to charge each drop to a predetermined level by applying a voltage signal just prior to drop detachment and terminating it just after. The drops then pass between a pair of deflection plates to which a fixed potential is applied. As the drops pass between the deflection plates, they are deflected from a straight line path by an amount determined by the amplitude of the charge placed upon each drop by the charging electrode. The drops are then either directed by a gutter into a waste reservoir or continue on and strike a print surface.
2. Description of the Prior Art
It is known in the art to form the head structure from a glass tube or similar material. Examples of such head structures are disclosed in U.S. Pat. Nos. 3,683,396 to Keur, et al., 3,929,071 to Cialone, et al. and 3,972,474 to Keur. In each of the above patents, a cylindrical piezoelectric driver element is utilized. Such a cylindrical element is relatively difficult to produce and therefore increases the cost of the head structure.
Many systems do in fact use a flat piezoelectric driver unit. Examples of such systems may be found in U.S. Pat. Nos. 3,946,398 to Kyser, et al., 4,074,284 to Dexter, et al. and 4,007,464 to Bassous, et al. However, these systems do not employ a tubular structure and are relatively complex.
In addition to the design of the head structure itself, a separate nozzle plate is usually required in order to insure an accurate orifice, and thereby accurately control drop size. Bonding of the nozzle plate to the head structure in the past has been done either by using an intermediate bonding agent or by use of a mechanical coupling.